Advanced vehicle technologies demand improved protection of transmission, gear and axle hardware. Conventional transmission, gear, and axle lubricants contain relatively high concentrations of sulfur containing lubricant additives are commonly used as anti-wear and extreme pressure additives to protect hardware. Unfortunately, these anti-wear and extreme pressure additives often provide variable protection while introducing undesirable consequences. For example, sophisticated electronic components, as well as rubber seals, can fail prematurely because of interactions with sulfur-containing compounds. As a result, new standards are expected for transmission, gear and axle lubricants, including dual clutch transmissions, continuously variable transmissions, electric transmissions and hybrid transmissions. The new standards are expected to require lower sulfur concentrations in the lubricants. Thus, there is a need for sufficient hardware protection without relying on harmful sulfur-containing additives.
It would be desirable to reduce or eliminate sulfur from lubricant compositions. Boron-containing compounds can provide anti-wear protection that may improve on gear scuffing. For example, in some cases boric acid is used as an anti-wear component. However, boric acid suffers from the disadvantage that it is not oil soluble and thus special steps, such as capping a dispersant with boric acid, must be taken in the lubricant manufacturing process to dissolve boric acid in the lubricant composition.
The present disclosure seeks to reduce or eliminate sulfur from the lubricant composition while providing simplified manufacturing process that does not require dissolution of oil insoluble components such as boric acid into the lubricant. In addition, the present disclosure provides lubricant additive combinations that have improved performance relative to lubricant compositions that employ boric acid-capped dispersants. In addition, the lubricant additive combinations of the present invention can be used at relatively lower treat rates.
A lubricating composition with improved storage stability comprising a major amount of an oil of lubricating viscosity, at least one alkali metal borate, at least one polysulfide mixture having at least 40% dihydrocarbyl tetrasulfide or higher sulfides, and at least one non-acidic phosphorus compound comprised of a trihydrocarbyl phosphate and a dihydrocarbyl dithiophosphate derivative is disclosed in US 2006/0252656 A1. Similarly, a lubricating oil composition having improved storage stability and load-carrying effect is disclosed in US 2006/0252657 A1. The composition comprises four components: (1) an alkali metal borate; (2) an oil-soluble sulfur compound; (3) a trialkyl phosphite; and (4) a mixture of greater than 50% neutralized acidic phosphates that are essentially free of monothiophosphates. These compositions suffer from the disadvantage of employing oil insoluble alkali metal borates.
Many of the additives used in transmission, gear and axle lubricants are multifunctional and there is often a conflict generated between properties, such as the scuffing load capacity, copper corrosion performance and bearing pitting performance. These conflicts inevitably mean that additives must be carefully selected and balanced. Accordingly, it has proven difficult for additive companies to meet performance requirements, much less improve significantly on any of the performance thresholds.
An object of the present disclosure is to provide an alternative to sulfur containing compounds by combining an amine salt of a hydrocarbyl acid phosphate and an oil-soluble borate to provide improved wear protection for lubrication of transmissions. The disclosure may provide a lubricant composition that has one or more of an improved scuffing load capacity as well as uses of and methods of using the lubricating composition to lubricate a transmission and/or reduce gear scuffing.